Abstract

Nitrogen (N) is known to influence the growth of Neonectria ditissima (N.d.), the causal organism of European canker. In vitro, inorganic N inhibits conidia germination at N concentrations above 0.2 mol/L while, in planta, foliar urea application increased disease expression of leaf scar wounds up to nine-fold. The influence of organic and inorganic N sources on mycelial growth and spore production of N.d.in vitro was investigated. Four organic and six inorganic N sources were tested on agar at concentrations of N between 0 and 0.2 mol/L, with 3 different N.d. isolates. Spore production was generally increased by the addition of low concentrations of N, with varying results at higher concentrations dependent on the N source; however, this also differed among N.d. isolates. Spore production was generally incompletely inhibited at the higher N concentrations tested. However, germination from the resulting conidia decreased, possibly due to morphological changes to the spores. Mycelial growth generally decreased with the addition of N. Understanding the N effect in planta will be further complicated by the physiological plant-N and plant-pathogen interaction processes.